2007-07-16 23:46:12 · 8 answers · asked by Anonymous in Science & Mathematics ➔ Astronomy & Space
Because the Earth does not happen to be moving at the one exact speed required for a circular orbit. In January, it is going a little too fast, which causes it to want to orbit out farther from the Sun. As it moves out farther, it slows down until in July it is farther from the Sun but now going a little too slow. That causes it to want to orbit in closer to the Sun. As it gets closer, it speeds up. It ends up where it started in January, too close to the Sun and going too fast, and the process repeats forever.
And yes, Earth is closest to the Sun in January, which is winter in the northern hemisphere. But it is summer in the southern hemisphere. The seasons are caused by the tilt of the Earth's rotational axis and not by the very small changes in distance from the Sun.
2007-07-17 02:36:03 · answer #1 · answered by campbelp2002 7 · 0⤊ 0⤋
The interaction of our planet with the other planets has caused this over a huge amount of time, and it will keep on a changin given more time. But for all it has changed to give the tiny little elliptic eccentricity, it won't be much a long way down the road, though I would think that once the elliptic orbit begins it will become more so to a greater degree in less time, but nothing to worry about, a bit of an ice age might be just what we need.
2007-07-17 06:54:58 · answer #2 · answered by mike453683 5 · 0⤊ 1⤋
Basically, since the earth's being pulled in towards the centre all the time by gravity, if it were going just the *right* speed, then it would go in a perfectly circular orbit. The gravitational effect would be pulling it inwards, but like any spinning object, its speed will make it try to shoot off out of its circle.
Since it isn't going exactly the right speed, it doesn't travel in a perfect circle, but instead in an ellipse.
(Note that this is a simplified account, but I think it gets the 'feel' across.)
2007-07-17 07:08:10 · answer #3 · answered by Anonymous · 0⤊ 0⤋
the general solution to orbital motion is an elipse. Circular motion is a special case needing special conditions to be met.
2007-07-17 07:49:44 · answer #4 · answered by Professional Physicist 3 · 0⤊ 0⤋
There are no circular orbits.
2007-07-17 10:05:23 · answer #5 · answered by JOHNNIE B 7 · 0⤊ 0⤋
It appears circular to our eyes.
2007-07-20 12:07:16 · answer #6 · answered by baba 5 · 0⤊ 0⤋
For season changes
2007-07-17 06:48:45 · answer #7 · answered by Architect 2 · 0⤊ 0⤋
when you meet your creator ask him as only he knows.
2007-07-17 15:17:50 · answer #8 · answered by Anonymous · 0⤊ 0⤋